As the world population continues to increase, more pressure is exerted on the availability of natural resources, including petroleum. Sustainable feedstocks are becoming more important and the functionality of these feedstocks provides both challenges and opportunities. Polymers account for approximately 7% of total petroleum use and thus represent important targets for sustainable chemistry. Over the last several years a number of researchers have investigated the conversion of renewable phenols from lignin and other biomass sources to bisphenols and derivative polymers. These renewable bisphenols can be converted to a wide variety of resins including polycarbonates and epoxy resins.
Cyclic terpenes are another important source of renewable phenols. Although not as abundant as lignin, naturally occurring terpenoids, including p-cymene, α- and β-pinene, are readily available in the form of turpentine. Approximately 350,000 tons of turpentine are produced annually with most of it generated as a byproduct of paper production. Limonene is another important terpene which is found in the skins of citrus fruit. Approximately 77 million kg of limonene are generated annually, primarily as a byproduct of orange juice production. In addition to isolation from trees and other organic matter, terpenoids are readily accessible via biosynthetic routes in which metabolically engineered organisms produce the molecules from sugar substrates. Utilization of lignocellulosic sugars and implementation of this approach on an industrial scale could legitimately allow for terpenoids to supplant various petroleum-based polymer feedstocks.
Terpenes are incredibly versatile molecules for the generation of polymers. The reactive double bonds of terpenes such as β-pinene allow for direct polymerization, while aromatic molecules such as p-cymene can be accessed via dehydrogenation. Similarly, phenolic terpenoids such as carvacrol and thymol can be readily generated from terpenes by selective oxidation and isomerization reactions. Carvacrol is a component of the essential oils of thyme and oregano and has previously been synthesized by a number of routes starting from various terpenoids (FIG. 1). One of the early routes involved reaction of p-cymene with concentrated sulfuric acid to generate the sulfonic acid salt. This salt was then fused with sodium hydroxide to generate carvacrol. Another route could start by oxidation of limonene to carvone followed by isomerization to carvacrol with sulfated zirconia. The classic route to carvone uses NOCl as the oxidizing agent, but more recently, highly selective oxidation of limonene to carvone has been accomplished using a Cr-based MOF catalyst and tert-butyl hydrogen peroxide as the oxidant. Limonene can also be selectively oxidized to 1,2-limonene oxide which is readily isomerized to dihydrocarvone. Dihydrocarvone can then be oxidized to carvacrol with reagents including ferric chloride.
The present invention provides novel bisphenols and novel methods for producing bisphenols and their products from renewable feedstocks
In addition to the issue of finding renewable sources for resins, there are problems with resins when exposed to water. This is a major problem for resins used in naval ships, vehicles, and structures. This arises because water interactions with epoxy resins, for example, can degrade the mechanical properties of the resins. Water can cause the resins to swell and to produce what is called “crazing” of the surfaces. Water absorbed in the resins can reduce the glass transition temperature (Tg) of the polymers and make them weaker. When polymers are utilized in composite materials, high water uptake coupled with rapid heating can lead to delamination of composite panels and parts. For example, in high performance aircraft, where surface operating temperatures (particularly the leading edges) can reach well above 100° C. at high speeds, conventional epoxy resins no longer offer adequate performance.
Resins and polymers made using the bisphenols of the present invention and their derivatives address this issue by exhibiting both low water uptake and high Tg.
It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not to be viewed as being restrictive of the invention, as claimed. Further advantages of this invention will be apparent after a review of the following detailed description of the disclosed embodiments, which are illustrated schematically in the accompanying drawings and in the appended claims.